Friday, 29 March, 2024
HomeHarm ReductionFrequent adolescent cannabis use linked to IQ decline — Irish Royal College

Frequent adolescent cannabis use linked to IQ decline — Irish Royal College

A study from the Royal College of Surgeons in Ireland has found that adolescents who frequently use cannabis may experience a decline in intelligence quotient (IQ) over time. The findings of the research provide further insight into the harmful neurological and cognitive effects of frequent cannabis use on young people.

The paper, led by researchers at the RCSI University of Medicine and Health Sciences, was published on 27 January 2021 in the journal Psychological Medicine.

The results revealed that there were declines of approximately two IQ points over time in those who use cannabis frequently compared to those who didn’t use cannabis.

Further analysis suggested that this decline in IQ points was primarily related to reduction in verbal IQ.

The research involved systematic review and statistical analysis on seven longitudinal studies involving 808 young people who used cannabis at least weekly for a minimum of six months and 5,308 young people who did not use cannabis.

In order to be included in the analysis, each study had to have a baseline IQ score prior to starting cannabis use and another IQ score at follow-up. The young people were followed up until age 18 on average, although one study followed the young people until age 38.

“Previous research tells us that young people who use cannabis frequently have worse outcomes in life than their peers and are at increased risk for serious mental illnesses like schizophrenia,” commented senior author of the paper Professor Mary Cannon, Professor of Psychiatric Epidemiology and Youth Mental Health at RCSI.

“Loss of IQ points early in life could have significant effects on performance in school and college and later employment prospects.

Dr Emmet Power, Clinical Research Fellow at RCSI and first author on the study, said: “Cannabis use during youth is of great concern as the developing brain may be particularly susceptible to harm during this period. The findings of this study help us to further understand this important public health issue.”

The study was carried out by researchers from the Department of Psychiatry, RCSI and Beaumont Hospital in Dublin.

The research was funded by a YouLead Collaborative Doctoral Award from the Health Research Board (Ireland) and a European Research Council Consolidator Award.

 

Intelligence quotient decline following frequent or dependent cannabis use in youth: A systematic review and meta-analysis of longitudinal studies

Emmet Power, Dr, Sophie Sabherwal, Dr Colm Healy, Dr Aisling O’Neill and Professor David Cotter and Mary Cannon.

Author affiliation: Royal College of Surgeons in Ireland

Published in the journal Psychological Medicine. Published online by Cambridge University Press on 27 January 2021.

 

Abstract

Previous systematic reviews and meta-analyses of cross-sectional data assessing the effect of cannabis on cognitive functioning and intelligence show inconsistent results. We hypothesised that frequent and dependent cannabis use in youth would be associated with Intelligence Quotient (IQ) decline.

This study is a systematic review and meta-analysis. We searched Embase, PubMed and PsychInfo from inception to 24 January 2020. We included studies with non-treatment seeking samples and pre- and post-exposure measures of IQ.

We requested data from authors if summary data was not available from published work. We preregistered our review with PROSPERO (ID no. CRD42019125624). We found seven cohort studies including 808 cases and 5,308 controls.

We found a significant effect for the association between frequent or dependent cannabis use in youth and IQ change, Cohen's d = −0.132 (95% CI −0.198 to −0.066) p < 0.001. Statistical heterogeneity between studies was also low at I2 = 0.2%.

Study quality was moderate to high. This translates to an average decline of approximately 2 IQ points following exposure to cannabis in youth. Future studies should have longer periods of follow up to assess the magnitude of developmental impact.

 

[link url="https://www.rcsi.com/dublin/news-and-events/news/news-article/2021/01/frequent-cannabis-use-by-young-people-linked-to-decline-in-iq"]Royal College of Surgeons in Ireland material – Frequent cannabis use by young people linked to decline in IQ (Open access)[/link]

 

[link url="https://www.cambridge.org/core/journals/psychological-medicine/article/intelligence-quotient-decline-following-frequent-or-dependent-cannabis-use-in-youth-a-systematic-review-and-metaanalysis-of-longitudinal-studies/26BEC9CBD2A39010C26100278F8CA813#"]Psychological Medicine article – Intelligence quotient decline following frequent or dependent cannabis use in youth: a systematic review and meta-analysis of longitudinal studies (Open access)[/link]

 

See also from MedicalBrief’s archives

 

[link url="https://www.medicalbrief.co.za/archives/cannabis-abuse-by-us-youth-with-mood-disorders-linked-to-self-harm-death/"]Cannabis abuse by US youth with mood disorders linked to self-harm, death[/link]

 

[link url="https://www.medicalbrief.co.za/archives/we-should-not-allow-a-cannabis-free-for-all-yale-ethicist/"]We should not allow a cannabis free-for-all – Yale ethicist[/link]

 

[link url="https://www.medicalbrief.co.za/archives/united-nations-and-united-states-reclassify-cannabis-as-less-risky-narcotic/"]United Nations – and United States – reclassify cannabis as less risky narcotic[/link]

 

 

MedicalBrief — our free weekly e-newsletter

We'd appreciate as much information as possible, however only an email address is required.